Bridge research: leading the way to the future

Public Roads, Summer, 1995 by James D. Cooper, Eric Munley

The continued economic strength and growth of the United States is intimately linked to the strength and reliability of our highways and bridges. The American public is experiencing the effects of an aging and deteriorating highway system. Increased delay, discomfort, and congestion, along with reductions in safety and service, are frequent. Highway agencies are struggling to cope with the increasing demands on their highways, and deteriorating bridges are becoming more severe choke points in the system.

There is an argument that the government should play a more vigorous role in promoting new technology. Clearly, standing still technologically is, in fact, an invitation to lose the technological and competitive edge. There are many forces at work that can erode the productivity gained by past advances in technology.

Transportation is an overhead cost (about 20 percent) of all goods and services in this country. Any reduction in that overhead is a general gain, freeing resources to produce other goods and services or allowing better distribution of those goods and services for the same cost. Research is an essential part of this reduction.

Unfortunately, research is often reactive, conducted in response to emergencies. In December 1967, a "new" technical issue emerged tragically with the loss of 46 lives in the collapse of the Silver Bridge between Point Pleasant, W.Va., and Gallipolis, Ohio. Even though structures such as the Silver Bridge have been the subject of investigation for some time, the issues of fatigue, fracture, and fracture-critical members suddenly demanded an accelerated search for answers.

A few more names from the recent past - Mianus River Bridge, Hatchie River Bridge, Schoharie Creek Bridge, and the San Francisco-Oakland Bay Bridge - bring to mind a chain of events: a spectacular and tragic collapse, extensive media coverage, congressional inquiry and detailed investigation, and calls to make the technical issue involved a top priority in research and implementation.

In many of these cases, the problems were foreseen, and warnings were sounded by one or more alert structural engineers. However, potential solutions were delayed by either the excessive costs imposed by existing technology or the reluctance to adopt new technology. In some of these cases, improved inspection technology would have allowed the problems to be spotted in time.

As a minimum, our goal is to break that chain of failures by conducting a proactive research program that provides solutions that can be implemented prior to the catastrophic failure.

The key to improving highways in the 21st century will be the use of advanced or enhanced materials, inspection technology, design procedures, construction methods, operational practices, maintenance and rehabilitation technology, and management techniques. We must use technology that permits rapid repair and return to service with minimal disruptions to safety and traffic flow. The challenge to develop and implement this technology must be undertaken in partnership with the entire highway community - government at all levels, universities, highway users, the construction industry, and heavy vehicle manufacturers. The highway community must shift gears in the highway program to anticipate and meet system shortcomings before they further impair service.

Thus, we need to give research and implementation a higher priority; to back that priority up with dollars; and to anticipate emerging issues and problems. Today's actions are not sufficient to address current problems and needs. But do we know or accept the value of research? Is the value of research quantifiable? Perhaps one can gain insight by examining the status of the nation's bridges, estimating the research investment for bridges, quantifying some specific cases or values of bridge research, and then drawing some conclusions.

Status of the Nation's Bridges

The 1993 report of the secretary of transportation to the U.S. Congress on the status of the nation's bridges concludes that, although bridge conditions are improving slightly, approximately 35 percent of the bridges in the United States are classified as deficient - either structurally deficient (21 percent) or functionally obsolete (14 percent).(1,2) This compares to 37 percent, 21 percent, and 16 percent, respectively, in the 1991 report.

Structural deficiency does not necessarily imply that a bridge is unsafe. It does, however, mean that a structure is unable to carry the vehicle loads or tolerate the speeds that would normally be expected for that particular bridge in its designated system. Functional obsolescence means that the bridge has inadequate width or vertical clearance for its associated highway system. In some cases, bridges become functionally obsolete because of highway improvements on the approaches to the bridge, such as lane additions or widening of approaching roads. In other cases, a bridge may be classified as functionally obsolete through a redefinition of desired standards.